Display device

ABSTRACT

To provide a display device including a flexible panel that can be handled without seriously damaging a driver circuit or a connecting portion between circuits. The display device includes a bent portion obtained by bending an element substrate. A circuit for driving the display device is provided in the bent portion and a wiring extends from the circuit, whereby the strength of a portion including the circuit for driving the display device is increased and failure of the circuit is reduced. Furthermore, the element substrate is bent in a connecting portion between an external terminal electrode and an external connecting wiring (FPC) so that the element substrate provided with the external terminal electrode fits the external connecting wiring, whereby the strength of the connecting portion is increased.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a display device.

2. Description of the Related Art

In recent years, with the development of digitization techniques, textdata and image data of newspapers, magazines, and the like have beenprovided as electronic data. This kind of electronic data is generallydisplayed on a display device incorporated in a personal computer or thelike, so that the content of the data can be read.

However, the display device incorporated in a personal computer or thelike is largely different from paper media like newspapers andmagazines, and has a problem of inconvenience such as difficulty incarrying.

In order to solve the above problem due to a difference in conveniencebetween electronic data and paper media, electronic paper havingflexibility has been proposed (for example, see Patent Document 1). Inthe case where an element such as a transistor is used in a displayportion of the flexible electronic paper, it is necessary to provide acircuit for driving the transistor, and in that case, the circuit may bedamaged when the electronic paper is bent (curved). Also in the casewhere an element such as a transistor is used in a display portion ofthe flexible electronic paper, the bending of the electronic paper maybe limited by the driver circuit.

REFERENCE Patent Document

-   [Patent Document 1] Japanese Published Patent Application No.    2003-337353

SUMMARY OF THE INVENTION

An object of one embodiment of the disclosed invention is to provide adisplay device including a flexible panel that can be handled withoutseriously damaging a driver circuit or a connecting portion betweencircuits.

One embodiment of the disclosed invention is a display device includinga bent portion obtained by bending an element substrate. A circuit fordriving the display device is provided in the bent portion and a wiringextends from the circuit, whereby the strength of a portion includingthe circuit for driving the display device is increased and failure ofthe circuit is reduced. Furthermore, the element substrate is bent in aconnecting portion between an external terminal electrode and anexternal connecting wiring (FPC) so that the edge of the substrateprovided with the external terminal electrode fits the externalconnecting wiring, whereby the strength of the connecting portion isincreased.

One embodiment of the disclosed invention is a display device includingan element substrate having flexibility, a display portion provided overthe element substrate, and a bent portion obtained by bending theelement substrate. The bent portion includes a driver circuit fordriving the display portion.

One embodiment of the disclosed invention is a display device includingan element substrate having flexibility, a sealing substrate havingflexibility, a display portion provided over the element substrate, anda bent portion obtained by bending the element substrate. The bentportion includes a driver circuit for driving the display portion, andthe element substrate is provided to be larger than the sealingsubstrate.

The display device of one embodiment of the disclosed invention mayinclude a supporting portion which holds and fixes the elementsubstrate.

In the display device of one embodiment of the disclosed invention, thebent portion is provided in a direction perpendicular or parallel to thelong axis of the supporting portion.

In the display device of one embodiment of the disclosed invention, thedriver circuit and the display portion may include a thin filmtransistor formed over the element substrate.

In the display device of one embodiment of the disclosed invention, theelement substrate may include an outer edge portion and a curvedportion, and the driver circuit may be provided between the outer edgeportion and the curved portion.

In the display device of one embodiment of the disclosed invention, theelement substrate may include a curved portion, and the driver circuitmay be provided between the display portion and the curved portion.

One embodiment of the disclosed invention is a display device includingan element substrate having flexibility, a display portion provided overthe element substrate, a supporting portion which holds and fixes theelement substrate, and a bent portion obtained by bending the elementsubstrate and included in the supporting portion. The bent portionincludes an external connecting electrode, and the external connectingelectrode fits an external connecting wiring.

One embodiment of the disclosed invention is a display device includingan element substrate having flexibility, a sealing substrate havingflexibility, a display portion provided over the element substrate, asupporting portion which holds and fixes the element substrate, and abent portion obtained by bending the element substrate and included inthe supporting portion. The element substrate is provided to be largerthan the sealing substrate. The bent portion includes an externalconnecting electrode, and the external connecting electrode fits anexternal connecting wiring.

In the display device of one embodiment of the disclosed invention, thesupporting portion may include a driver circuit for driving the displayportion, and the driver circuit may be electrically connected to theexternal connecting wiring.

In the display device of one embodiment of the disclosed invention, adisplay element included in the display portion may be anelectrophoretic element, a liquid crystal element, or a light-emittingelement.

According to one embodiment of the disclosed invention, it is possibleto provide a robust display device having a driver circuit or aconnecting portion between circuits which is unlikely to be damaged.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A and 1B are perspective views illustrating one embodiment of thepresent invention;

FIG. 2 is a perspective view illustrating one embodiment of the presentinvention;

FIG. 3A is a top view and FIGS. 3B and 3C are cross-sectional viewsillustrating one embodiment of the present invention;

FIGS. 4A to 4C are cross-sectional views illustrating one embodiment ofthe present invention;

FIG. 5A is a perspective view and FIGS. 5B and 5C are cross-sectionalviews illustrating one embodiment of the present invention;

FIGS. 6A and 6B are respectively a perspective view and across-sectional view illustrating one embodiment of the presentinvention;

FIGS. 7A and 7B are cross-sectional views illustrating one embodiment ofthe present invention;

FIGS. 8A and 8B are cross-sectional views illustrating one embodiment ofthe present invention;

FIG. 9 is a cross-sectional view illustrating one embodiment of thepresent invention;

FIGS. 10A and 10B are respectively a perspective view and across-sectional view illustrating one embodiment of the presentinvention;

FIG. 11 is a cross-sectional view illustrating one embodiment of thepresent invention;

FIGS. 12A and 12B are cross-sectional views illustrating one embodimentof the present invention;

FIGS. 13A to 13D are cross-sectional views illustrating one embodimentof the present invention;

FIGS. 14A and 14B are views illustrating electronic appliances of oneembodiment of the present invention; and

FIGS. 15A and 15B are views illustrating electronic appliances of oneembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be described in detail withreference to drawings. Note that the present invention is not limited tothe description below, and it is apparent to those skilled in the artthat modes and details can be modified in various ways without departingfrom the spirit and scope of the invention disclosed in thisspecification and the like. Furthermore, structures of differentembodiments can be implemented in appropriate combination. Note that inthe structures of the present invention described below, like portionsor portions having a similar function are denoted by like referencenumerals, and the description thereof is omitted.

Note that the size, the thickness of a layer, or a region of eachstructure illustrated in the drawings or the like in embodiments isexaggerated for clarity in some cases. Therefore, the scale is notnecessarily limited to that illustrated in the drawings.

Note that the numeral terms such as “first”, “second”, and “third” inthis specification are used in order to avoid confusion betweencomponents and do not set a limitation on number.

Embodiment 1

A structure disclosed in this embodiment will be schematically describedwith reference to FIGS. 1A and 1B and FIGS. 5A to 5C.

A display device shown in this embodiment includes an element substratehaving flexibility, a display portion provided over the elementsubstrate, a supporting portion which holds and fixes a side of theelement substrate having flexibility (in a manner that prevents itsmovement), and a bent portion obtained by bending the element substrate.The bent portion includes a driver circuit for driving the displayportion, such as a scan line driver circuit. The supporting portionincludes, for example, a signal line driver circuit that outputs asignal to a signal line.

FIGS. 1A and 1B illustrate an example of the display device, whichincludes a supporting portion 102 provided on a side of an elementsubstrate 101. The structure of the display device will be specificallydescribed below with reference to FIGS. 1A and 1B. Note that FIG. 1A isa perspective view of the top surface of the display device on which thedisplay portion is formed, and FIG. 1B is a perspective view of the backsurface of the display device.

The display device illustrated in FIGS. 1A and 1B includes the elementsubstrate 101 on which the display portion 103 is provided, thesupporting portion 102 that holds and fixes a side of the elementsubstrate 101, a driver circuit 108 that controls display of the displayportion 103 with scan lines (also referred to as a scan line drivercircuit 108), and a driver circuit 106 that controls display of thedisplay portion 103 with signal lines (also referred to as a signal linedriver circuit 106). FIGS. 1A and 1B also illustrate a plurality of scanlines 105 extending from the scan line driver circuit 108, and aplurality of signal lines 104 extending from the signal line drivercircuit 106. The display device illustrated in FIGS. 1A and 1B is adisplay device having flexibility, and the scan line driver circuit 108is provided in a bent portion 107 on the back surface of the flexiblesubstrate (such as a plastic substrate) in FIG. 1B, and from the scanline driver circuit 108, the scan lines 105 extend to the displaysurface. Although not illustrated in FIGS. 1A and 1B, a sealingsubstrate overlaps the element substrate 101. When the element substrate101 has a larger area than the sealing substrate, the bent portion 107can be formed only by the element substrate 101, resulting in areduction in the thickness of the bent portion 107. Thus, the use of theelement substrate 101 having a larger area than the sealing substrateallows, for example, the bent portion 107 to be bent more easily.

The scan line driver circuit 108 needs to be provided at least on thesurface of the element substrate 101. A plurality of scan line drivercircuits 108 may be provided on the element substrate 101. The signalline driver circuit 106 is preferably provided inside the supportingportion 102. Such a structure makes it possible to reduce damage on thesignal line driver circuit 106. For example, a prismatic or cylindricalhousing having a cavity is used for the supporting portion 102, and thesignal line driver circuit 106 can be provided in the cavity.Alternatively, a flat housing may be used for the supporting portion102; in that ease, the signal line driver circuit 106 can be provided tooverlap the housing (for example, to be in contact with the housing).

It is preferable that the supporting portion 102 be bent less than (morerigid than) at least the element substrate 101. For example, a plasticor metal housing with a greater thickness than the element substrate 101can be used for the supporting portion 102. In that case, the displaydevice except for the supporting portion 102 can be bent.

The supporting portion 102 may be provided at any place; for example,the supporting portion 102 can be provided along a side of the elementsubstrate 101. In the case where the element substrate 101 has arectangular shape as illustrated in FIGS. 1A and 1B, for example, thesupporting portion 102 can be provided along a predetermined side (so asto fix the side). Note that the “rectangular shape” here includes ashape with a rounded corner. There is no particular limitation on thesize or shape of the supporting portion 102.

As illustrated in FIGS. 1A and 1B, the scan line driver circuit 108 isprovided in the bent portion 107 that is in a direction perpendicular tothe long axis of the supporting portion 102. The scan lines 105connected to the scan line driver circuit 108 in the bent portion 107extend from the back surface to the top surface of the elementsubstrate. Accordingly, the scan line driver circuit 108 is provided ina region where the element substrate 101 is bent toward the back surfaceto be folded, whereby the scan line driver circuit 108 can be increasedin strength so as not to be easily damaged; thus, a robust displaydevice can be obtained. In addition, the bent portion formed by bendingthe flexible substrate includes a curved portion (a portion having arounded and curved shape) obtained by the bending the element substrate,which makes it possible to reduce injury of the user caused by a slip ofa finger or the like.

The bent portion 107 corresponds to a region formed by bending theelement substrate 101. In the bent portion 107, an outer edge portion ofthe bent element substrate 101 may be fixed by being attached to theelement substrate 101 or by being fastened by another component. Theouter edge portion means an end of the substrate.

The position of the bent portion 107 including the scan line drivercircuit 108 is not limited to that illustrated in FIGS. 1A and 1B. Forexample, as illustrated in FIG. 5A, an element substrate 501 may be benttoward the top surface of the element substrate 501 on which the displayportion 103 is formed, so that the scan line driver circuit 108 isprovided in the folded substrate in the bent portion 107. In thestructure illustrated in FIG. 5A, the scan line driver circuit 108 canbe provided inside the element substrate 501 and thus can be furtherincreased in strength so as not to be easily damaged; as a result, arobust display device can be obtained.

In the cross section of the bent portion 107 including the scan linedriver circuit 108 illustrated in FIGS. 1A and 1B and FIG. 5A, thedriver circuit 108 may be provided at least in a region where theelement substrate is bent to be folded. For example, as illustrated inFIG. 5B, the driver circuit 108 may be provided between a curved portion502 (a portion having a rounded and curved shape obtained by bending thesubstrate along the bent portion) and an outer edge portion 503 of theelement substrate. Alternatively, the driver circuit 108 may be providedbetween the curved portion 502 and a display portion 504.

Furthermore, where the scan line driver circuit 108 and a pixel circuitincluded in each pixel of the display portion 103 are manufactured inthe same process on a flexible substrate, cost reduction can beachieved.

The pixel circuits included in the display portion 103 and the scan linedriver circuit 108 can be formed using elements such as thin filmtransistors. On the other hand, a high-speed operating circuit such asthe signal line driver circuit 106 can be formed using an IC (integratedcircuit) which uses an SOI substrate or a semiconductor substrate suchas a silicon substrate, and the IC can be provided inside the supportingportion 102.

This embodiment can be implemented in appropriate combination with thestructures shown in the other embodiments.

Embodiment 2

A structure different from that shown in Embodiment 1 will be describedwith reference to FIG. 2, FIGS. 3A to 3C, and FIGS. 4A to 4C.

In a display device of this embodiment, as illustrated in FIG. 2, a bentportion 201 is provided on a side opposite to the supporting portion102, namely, in a direction parallel to the long axis of the supportingportion 102. In addition, as in the above embodiment, a curved portioncan be formed by bending the periphery of the element substrate havingflexibility, which makes it possible to reduce injury of the user causedby a slip of a finger or the like on the edge of the display device.

FIG. 3A is a top view of the display device, FIG. 3B is across-sectional view along line A-B of FIG. 3A, and FIG. 3C is anenlarged view of the cross section of FIG. 3B.

In the display device illustrated in FIG. 3A, a housing having a cavityis used for the supporting portion 102 and a signal line driver circuitis provided inside the housing. Here, the signal line driver circuit isprovided as an IC 303 that is formed inside the supporting portion 102.The IC 303 can be formed using an SOI substrate, a semiconductorsubstrate such as a silicon substrate, or the like. It is needless tosay that a circuit other than the signal line driver circuit (e.g., aCPU or a memory) can be included in the IC.

FIG. 3A illustrates the case where the IC 303 provided inside thesupporting portion 102 is mounted on an external connecting wiring (FPC:flexible printed circuit). More specifically, the IC 303 controlling thedisplay portion 103 is mounted on an external connecting wiring 301, andthe external connecting wiring 301 is electrically connected to aprinted board 302. In a connecting portion 304 where the externalconnecting wiring 301 is electrically connected to the display deviceincluding an element substrate 601 attached to a sealing substrate 603,the element substrate 601 having an external connecting electrode andthe external connecting wiring 301 are bent to fit each other asillustrated in FIGS. 3B and 3C, whereby the external connectingelectrode and the external connecting wiring 301 are electricallyconnected to each other. Accordingly, the contact area of terminals andthe adhesive strength of the connecting portion can be increased,whereby wrong connection between the terminals can be reduced and arobust display device can be obtained.

A flexible substrate such as a plastic substrate can be used as theelement substrate 601 and the sealing substrate 603. The flexiblesubstrate can be made of, for example, an aramid resin, a polyethylenenaphthalate (PEN) resin, a polyether sulfone (PES) resin, apolyphenylene sulfide (PPS) resin, or a polyimide (PI) resin. It is alsopossible to use a prepreg that is a structure body in which fiber isimpregnated with an organic resin.

Note that the connecting portion 304 may include a space 401 asillustrated in FIG. 4A, and the element substrate 601 and the externalconnecting wiring 301 may fit each other with a predetermined space leftin the connecting portion 304. The structure of FIG. 4A enlarges themovable part of the display device.

Alternatively, the element substrate 601 and the external connectingwiring 301 may fit each other in the connecting portion 304 so thatouter edge portions 402 are closely attached to each other asillustrated in FIG. 4B. The structure of FIG. 4B increases the adhesivestrength between the element substrate 601 and the external connectingwiring 301.

Further alternatively, in the connecting portion 304, the periphery ofthe area where the element substrate 601 is connected to the externalconnecting wiring 301 may be filled with a connecting member 403 asillustrated in FIG. 4C. The structure of FIG. 4C further increases theadhesive strength between the element substrate 601 and the externalconnecting wiring 301.

This embodiment can be implemented in appropriate combination with thestructures shown in the other embodiments.

Embodiment 3

In this embodiment, an example of the structure of the display devicewill be described with reference to perspective views andcross-sectional views.

As the display device, electronic paper using an electrophoretic elementas a display element, a light-emitting display device (anelectroluminescence (EL) panel), a liquid crystal display device, andthe like can be employed. The display device is a panel in which adisplay element is sealed. The panel includes a terminal electrode towhich a signal is externally supplied (an external terminal electrode),and a connector, e.g., an external connecting wiring such as a flexibleprinted circuit (FPC), a tape automated bonding (TAB) tape, or a tapecarrier package (TCP), is attached to the terminal electrode, wherebythe panel is electrically connected to an external circuit including adriver circuit. An IC including the driver circuit may be directlymounted on the display device by chip on glass (COG).

An embodiment of the display device will be described with reference toperspective views and cross-sectional views of FIGS. 6A and 6B, FIGS. 7Aand 7B, FIGS. 8A and 8B, FIG. 9, FIGS. 10A and 10B, and FIG. 11. FIG. 6Ais a perspective view of the display device illustrated in FIG. 1A. FIG.6B is a cross-sectional view along line A-B of FIG. 6A, whichillustrates a cross-sectional structure of the display portion 103 andthe bent portion 107. Note that FIG. 6A is similar to FIG. 1A, and theback surface of FIG. 6A is similar to FIG. 1B and therefore is notdescribed in detail here.

FIG. 6B is an example including the scan line driver circuit 108 and thedisplay portion 103 provided with a pixel circuit. The display portion103 and the scan line driver circuit 108 are sealed between the elementsubstrate 601 (also referred to as a first substrate) and the sealingsubstrate 603 (also referred to as a second substrate) with a sealingmember 602.

The display portion 103 and the scan line driver circuit 108 that areprovided on the element substrate 601 include a plurality of thin filmtransistors. FIG. 6B illustrates, for example, a thin film transistor604 included in the display portion 103 and a thin film transistor 605included in the scan line driver circuit 108. Insulating layers 606 and607 are provided on the thin film transistors 604 and 605. Note that aninsulating film serving as a base film may be provided under the thinfilm transistors 604 and 605.

There is no particular limitation on the kind of the thin filmtransistors 604 and 605, and various kinds of thin film transistors canbe employed. FIG. 6B illustrates an example in which aninverted-staggered thin film transistor with a bottom-gate structure isused as the thin film transistors 604 and 605. Although the thin filmtransistors 604 and 605 are of a channel-etched type, it is alsopossible to use a channel protective type inverted-staggered thin filmtransistor including a channel protective film on a semiconductor layer.Note that the semiconductor layer included in the thin film transistorcan be made of a semiconductor material such as an organicsemiconductor, a compound semiconductor, or an oxide semiconductor aswell as silicon or germanium. A thin film transistor using an organicsemiconductor as the semiconductor material has high resistant tobending and shock. When an organic material or a conductivehigh-molecular material is used for an insulating film and/or aconductive layer as well as the semiconductor layer, the resistance tobending and shock can be further increased.

The thin film transistor 604 included in the display portion 103 iselectrically connected to a display element, thereby constituting thedisplay device. There is no particular limitation on the kind of thedisplay element as long as display can be performed, and various kindsof display elements can be employed. FIG. 6B illustrates an example ofusing a twisting ball system which is a display method used forelectronic paper and using a twisting ball as the display element. Asanother display method used for electronic paper, there is anelectrophoresis system, a powder system (also called a toner display), aliquid crystal system, or the like. Electronic paper is advantageous inthat its readability is at the same level as that of paper, and itconsumes less power and is thinner and lighter than other displaydevices.

The twisting ball display system illustrated in FIG. 6B refers to amethod in which spherical particles each colored in black and white arearranged between electrode layers used for a display element, and apotential difference is generated between the electrode layers tocontrol the orientation of the spherical particles, so that display isperformed.

A spherical particle 612 includes a black region 610 a, a white region610 b, and a cavity 611 around the regions which is filled with liquid,and the spherical particle is provided between a first electrode layer608 connected to the thin film transistor 604 and a second electrodelayer 609 provided on the sealing substrate 603. A space around thespherical particle 612 is filled with a filler 613 such as a resin. Thesecond electrode layer 609 corresponds to a common electrode (a counterelectrode). The second electrode layer 609 is electrically connected toa common potential line.

The bent portion 107 obtained by bending the periphery of the displaydevice illustrated in FIGS. 6A and 6B has a cross section in which theouter edge of the bent element substrate 601 is covered with the bentsealing substrate 603. In other words, the curvature of the elementsubstrate 601 is larger than that of the sealing substrate 603. As aresult, the sealing substrate 603 can be provided with a curved portion614 which is bent and rounded, which makes it possible to reduce injuryof the user caused by a slip of a finger or the like.

Instead of the twisting ball, an electrophoretic element can be used asthe display element. FIG. 7A illustrates an example in which anelectrophoretic element is used as the display element in the displayportion 103. Note that similarly to FIG. 6B, FIG. 7A illustrates a crosssection of the display portion 103 that is sealed between the elementsubstrate 601 and the sealing substrate 603 with the sealing member 602.Accordingly, in FIG. 7A, structures similar to those in FIG. 6B are notillustrated and described. A microcapsule 703 having a diameter of about10 μm to 200 μm is used as a display element in FIG. 7A, and in themicrocapsule 703, a transparent liquid 701, a negatively charged blackmicroparticle 702 a as a first particle, and a positively charged whitemicroparticle 702 b as a second particle, are encapsulated.

In the microcapsule 703 that is provided between the first electrodelayer 608 and the second electrode layer 609, when an electric field isapplied between the first electrode layer 608 and the second electrodelayer 609, the white microparticle 702 b and the black microparticle 702a move to opposite sides from each other, so that white or black can bedisplayed. A display element using this principle is an electrophoreticdisplay element. The electrophoretic display element has highreflectivity; thus, an auxiliary light is not needed, power consumptionis low, and a display portion can be recognized in a dim place. Inaddition, even when power is not supplied to the display portion, animage which has been displayed once can be maintained. Accordingly, adisplayed image can be stored even if a display device is distanced froman electric wave source.

Note that the first particle and the second particle each containpigment and do not move without an electric field. Moreover, the colorsof the first particle and the second particle are different from eachother (the particles may be colorless).

A solution in which the aforementioned microcapsule 703 is dispersed ina solvent 704 is referred to as electronic ink. This electronic ink canbe printed on a surface of glass, plastic, cloth, paper, and the like.Furthermore, color display can also be achieved by using a color filteror pigment particles.

Note that the first particle and the second particle in the microcapsule703 may be formed of one or plural kinds of the following materials: aconductive material, an insulating material, a semiconductor material, amagnetic material, a liquid crystal material, a ferroelectric material,an electroluminescent material, an electrochromic material, and amagnetophoretic material.

Electronic Liquid Powder (registered trademark) may be used for a powdersystem. An example of using Electronic Liquid Powder as the displayelement is illustrated in FIG. 7B. Note that similarly to FIG. 6B, FIG.7B illustrates a cross section of the display portion 103 that is sealedbetween the element substrate 601 and the sealing substrate 603 with thesealing member 602. A positively charged black liquid powder 753 a and anegatively charged white liquid powder 753 b are contained in a space752 segmented by the first electrode layer 608, the second electrodelayer 609, and a rib 751. Note that the space 752 is filled with air.

When an electric field is applied between the first electrode layer 608and the second electrode layer 609, the black liquid powder 753 a andthe white liquid powder 753 b move to opposite sides, so that white orblack can be displayed. As the liquid powders, color powders of red,yellow, blue, or the like may be used.

A light-emitting element utilizing electroluminescence (an EL element)may also be used as the display element. Light-emitting elementsutilizing electroluminescence are classified according to whether alight-emitting material is an organic compound or an inorganic compound.In general, the former is referred to as an organic EL element, and thelatter is referred to as an inorganic EL element.

In an organic EL element, by application of voltage to a light-emittingelement, electrons and holes are separately injected from a pair ofelectrodes into a layer containing a light-emitting organic compound,and current flows. Then, the carriers (electrons and holes) arerecombined, so that the light-emitting organic compound is excited. Thelight-emitting organic compound returns to a ground state from theexcited state, thereby emitting light. Owing to such a mechanism, thislight-emitting element is referred to as a current-excitationlight-emitting element.

The inorganic EL elements are classified according to their elementstructures into a dispersion-type inorganic EL element and a thin-filminorganic EL element. A dispersion-type inorganic EL element has alight-emitting layer where particles of a light-emitting material aredispersed in a binder, and its light emission mechanism isdonor-acceptor recombination type light emission that utilizes a donorlevel and an acceptor level. A thin-film inorganic EL element has astructure in which a light-emitting layer is sandwiched betweendielectric layers, which are further sandwiched between electrodes, andits light emission mechanism is localized type light emission thatutilizes inner-shell electron transition of metal ions. Description ismade here using an organic EL element as a light-emitting element.

In order to extract light emitted from the light-emitting element, atleast one of a pair of electrodes is required to transmit light. A thinfilm transistor and a light-emitting element are formed over asubstrate. The light-emitting element can have any of the followingstructures: a top emission structure in which light is extracted throughthe surface opposite to the substrate; a bottom emission structure inwhich light is extracted through the surface on the substrate side; anda dual emission structure in which light is extracted through thesurface opposite to the substrate and the surface on the substrate side.

FIG. 8A illustrates an example of using a light-emitting display device(an EL panel) as a display device. Note that similarly to FIG. 6B, FIG.8A illustrates a cross section of the display portion 103 that is sealedbetween the element substrate 601 and the sealing substrate 603 with thesealing member 602. A light-emitting element 801 which is a displayelement is electrically connected to the thin film transistor 604provided in the display portion 103. Although the light-emitting element801 has a stacked structure of the first electrode layer 608, anelectroluminescent layer 802, and a second electrode layer 803, thestructure of the light-emitting element 801 is not limited to this. Thestructure of the light-emitting element 801 can be changed asappropriate depending on the direction in which light is extracted fromthe light-emitting element 801, or the like.

A partition wall 804 is made of an organic resin film, an inorganicinsulating film, or organic polysiloxane. It is particularly preferablethat the partition wall 804 be formed of a photosensitive material tohave an opening over the first electrode layer 608 so that a sidewall ofthe opening is formed as an inclined surface with continuous curvature.

The electroluminescent layer 802 may be formed as a single layer or aplurality of layers stacked.

In order to prevent entry of oxygen, hydrogen, moisture, carbon dioxide,or the like into the light-emitting element 801, a protective film maybe formed over the second electrode layer 803 and the partition wall804. As the protective film, a silicon nitride film, a silicon nitrideoxide film, a DLC film, or the like can be formed. A space sealed withthe element substrate 601, the sealing substrate 603, and the sealingmember 602 is provided with a filler 805 so as to be sealed tightly. Insuch a manner, the display device is preferably packaged (sealed) with aprotective film (such as a laminate film or an ultraviolet curable resinfilm) or a cover material with high air-tightness and littledegasification so that the panel is not exposed to the outside air.

As the filler 805, an ultraviolet curable resin or a thermosetting resinas well as an inert gas such as nitrogen or argon can be used. Forexample, PVC (polyvinyl chloride), acrylic, polyimide, an epoxy resin, asilicone resin, PVB (polyvinyl butyral), or EVA (ethylene vinyl acetate)can be used. For example, nitrogen may be used for the filler.

If needed, an optical film such as a polarizing plate, a circularlypolarizing plate (including an elliptically polarizing plate), aretardation plate (a quarter-wave plate or a half-wave plate), or acolor filter may be provided as appropriate on a light-emitting surfaceof the light-emitting element. Furthermore, the polarizing plate or thecircularly polarizing plate may be provided with an anti-reflectionfilm. For example, anti-glare treatment by which reflected light can bediffused by projections and depressions on the surface so as to reducethe glare can be performed.

FIG. 8B illustrates an example of using a liquid crystal display deviceas a display device. Note that similarly to FIG. 6B, FIG. 8B illustratesa cross section of the display portion 103 that is sealed between theelement substrate 601 and the sealing substrate 603 with the sealingmember 602. In FIG. 8B, a liquid crystal element 851 which is a displayelement includes the first electrode layer 608, the second electrodelayer 609, and a liquid crystal layer 852. An insulating film 853 and aninsulating film 854 serving as orientation films are provided to holdthe liquid crystal layer 852 therebetween. The second electrode layer609 is provided on the sealing substrate 603 side, and the firstelectrode layer 608 and the second electrode layer 609 are stacked withthe liquid crystal layer 852 interposed therebetween.

FIG. 8B also illustrates a columnar spacer 855 obtained by selectivelyetching an insulating film. The spacer 855 is provided to control thethickness of the liquid crystal layer 852 (the cell gap). Alternatively,a spherical spacer may be used.

Although not illustrated in the liquid crystal display device of FIG.8B, a color filter (a coloring layer), a black matrix (a light-shieldinglayer), an optical member (an optical substrate) such as a polarizingmember, a retardation member, or an anti-reflection member, and the likeare provided as appropriate. For example, circular polarization may beobtained by using a polarizing substrate and a retardation substrate. Inaddition, a backlight, a side light, or the like may be used as a lightsource. An EL panel is preferably used as the backlight in order toreduce the thickness of the display device.

Alternatively, a liquid crystal exhibiting a blue phase for which analignment film is unnecessary may be used. A blue phase is one of theliquid crystal phases, which is generated just before a cholestericphase changes into an isotropic phase while temperature of cholestericliquid crystal is increased. Since the blue phase is only generatedwithin a narrow range of temperature, a liquid crystal compositioncontaining a chiral agent at 5 wt % or more is used for the liquidcrystal layer 852 in order to increase the temperature range. The liquidcrystal composition which includes a liquid crystal exhibiting a bluephase and a chiral agent has a short response time of 10 μs to 100 μs,has optical isotropy, which makes the alignment process unneeded, andhas a small viewing angle dependence.

Although FIG. 8B illustrates an example of a transmissive liquid crystaldisplay device, an embodiment of the present invention can also beapplied to a reflective liquid crystal display device or a transflectiveliquid crystal display device.

In FIGS. 7A and 7B and FIGS. 8A and 8B, a plastic substrate havinglight-transmitting properties can be used as the element substrate 601and the sealing substrate 603. As plastic, a fiberglass-reinforcedplastics (FRP) plate, a polyvinyl fluoride (PVF) film, a polyester film,or an acrylic resin film can be used. Alternatively, a sheet with astructure in which an aluminum foil is sandwiched between PVF films orpolyester films can be used.

Note that an insulating layer serving as a protective film may beprovided over the thin film transistor 604. The protective film isprovided to prevent entry of impurities floating in the air, such as anorganic substance, a metal substance, or moisture, and is preferably adense film. The protective film may be formed by sputtering to be asingle-layer film or a multi-layer film of a silicon oxide film, asilicon nitride film, a silicon oxynitride film, a silicon nitride oxidefilm, an aluminum oxide film, an aluminum nitride film, an aluminumoxynitride film, and an aluminum nitride oxide film.

The insulating layer 607 serving as a planarizing insulating film can bemade of an organic material having heat resistance, such as polyimide,acrylic, benzocyclobutene, polyamide, or epoxy. Other than such organicmaterials, it is also possible to use a low-dielectric constant material(a low-k material), a siloxane-based resin, PSG (phosphosilicate glass),BPSG (borophosphosilicate glass), or the like. The insulating layer maybe formed by stacking a plurality of insulating films made of thesematerials.

There is no particular limitation on the method for forming theinsulating layer 607, and the insulating layer 607 can be formed,depending on the material, by sputtering, SOG, spin coating, dipping,spray coating, droplet discharging (e.g. ink-jet, screen printing, oroffset printing), doctor knife, roll coater, curtain coater, knifecoater, or the like. In the case where the insulating layer is formedusing a material solution, the semiconductor layer may be annealed (at200° C. to 400° C.) at the same time as a baking step. When the step ofbaking the insulating layer serves to anneal the semiconductor layer,the display device can be efficiently manufactured.

The display device displays an image by transmitting light from a lightsource or a display element. Therefore, the substrates and the thinfilms such as insulating films and conductive films provided in thedisplay portion through which light passes have light-transmittingproperties in the visible wavelength range.

The first electrode layer and the second electrode layer (also referredto as a pixel electrode layer, a common electrode layer, or a counterelectrode layer) for applying voltage to the display element may havelight-transmitting properties or light-reflecting properties dependingon the direction in which light is extracted, the place where theelectrode layer is provided, or the pattern structure of the electrodelayer.

The first electrode layer 608 and the second electrode layer 609 can bemade of a light-transmitting conductive material such as indium oxidecontaining tungsten oxide, indium zinc oxide containing tungsten oxide,indium oxide containing titanium oxide, indium tin oxide containingtitanium oxide, indium tin oxide (hereinafter referred to as ITO),indium zinc oxide, or indium tin oxide to which silicon oxide is added.

The first electrode layer 608 and the second electrode layer 609 canalso be made of one or more kinds of materials selected from a metalsuch as tungsten (W), molybdenum (Mo), zirconium (Zr), hafnium (Hf),vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), cobalt (Co),nickel (Ni), titanium (Ti), platinum (Pt), aluminum (Al), copper (Cu),and silver (Ag); an alloy of these metals; and a nitride of thesemetals.

Alternatively, a conductive composition containing a conductive highmolecule (also referred to as a conductive polymer) can be used for thefirst electrode layer 608 and the second electrode layer 609. As theconductive high molecule, a so-called π-electron conjugated conductivepolymer can be used. For example, it is possible to use polyaniline or aderivative thereof, polypyrrole or a derivative thereof, polythiopheneor a derivative thereof, or a copolymer of two or more kinds of them.

Since the thin film transistors are easily damaged by static electricityor the like, a protective circuit for protecting the driver circuit ispreferably provided. The protective circuit is preferably formed using anon-linear element.

FIG. 9 illustrates a cross-sectional structure of the display device,which is different from that illustrated in FIG. 6B. FIG. 9 illustratesa cross-sectional structure along line A-B of FIG. 6A, which isdifferent from that illustrated in FIG. 6B. FIG. 9 is different fromFIG. 6B in the following points: in the cross section of the bentportion 107, a display element held between the first electrode layer608 and the second electrode layer 609 in a region sealed with thesealing members 602, and the sealing substrate 603 are not formed andthe insulating layer 607 is covered with a sealing layer 901. In thebent portion 107, it is possible to eliminate the first electrode layer608, the second electrode layer 609, the sealing substrate 603, and thelike which contribute to display, so that the periphery of the displaydevice can be bent more easily.

FIGS. 10A and 10B illustrate a structure of the display device, which isdifferent from that illustrated in FIGS. 6A and 6B. FIG. 10A is aperspective view of the display device illustrated in FIG. 5A. FIG. 10Bis a cross-sectional view along line A-B of FIG. 10A, which illustratesa cross-sectional structure of the display portion 103 and the bentportion 107. Note that FIG. 10A is similar to FIG. 5A, and therefore isnot described in detail here. Further, the display portion 103 in FIG.10B has a structure similar to that of the display portion 103 in FIG.6B, and therefore is not described in detail here. A difference betweenthe structure of the bent portion 107 in FIG. 10B and that in FIG. 6B isthat the outer edge of the bent sealing substrate 603 is covered withthe bent element substrate 601. The other structure of the bent portion107 in FIG. 10B is similar to that in FIG. 6B, and therefore is notdescribed in detail here.

The bent portion 107 obtained by bending the periphery of the displaydevice illustrated in FIGS. 10A and 10B has a cross section in which theouter edge of the bent sealing substrate 603 is covered with the bentelement substrate 601. In other words, the curvature of the sealingsubstrate 603 is larger than that of the element substrate 601. As aresult, the element substrate 601 can be provided with the curvedportion 614 which is bent and rounded, which makes it possible to reduceinjury of the user caused by a slip of a finger or the like.

In FIG. 10B, as in FIGS. 7A and 7B and FIGS. 8A and 8B, anelectrophoretic element using a microcapsule, an electrophoretic elementof a powder system, a light-emitting element, or a liquid crystalelement can be used as the display element instead of the twisting ball.

FIG. 11 illustrates a cross-sectional structure of the display device,which is different from that illustrated in FIG. 10B. FIG. 11illustrates a cross-sectional structure along line A-B of FIG. 10A,which is different from that illustrated in FIG. 10B. FIG. 11 isdifferent from FIG. 10B in the following points: in the cross section ofthe bent portion 107, a display element held between the first electrodelayer 608 and the second electrode layer 609 in a region sealed with thesealing members 602, and the sealing substrate 603 are not formed andthe insulating layer 606 is covered with the sealing layer 901. In thebent portion 107, as in FIG. 9, it is possible to eliminate the firstelectrode layer 608, the second electrode layer 609, the sealingsubstrate 603, and the like which contribute to display, so that theperiphery of the display device can be bent more easily.

FIGS. 12A and 12B illustrate a structure of the display device, which isdifferent from that illustrated in FIGS. 6A and 6B and FIGS. 10A and10B. FIG. 12A is a cross-sectional view of the display deviceillustrated in FIG. 4C. FIG. 12B illustrates the cross-sectional view ofFIG. 12A in detail, and specifically, illustrates a cross-sectionalstructure of the display portion 103 and a bent portion 1201. Note thatFIG. 12A is similar to FIG. 4C, and therefore is not described in detailhere. Further, the display portion 103 in FIG. 12B has a structuresimilar to that of the display portion 103 in FIG. 6B and FIG. 10B, andtherefore is not described in detail here.

The structure of the bent portion 1201 in FIG. 12B will be described.The bent portion 1201 in FIG. 12B includes the element substrate 601extending from the display portion 103 and bent, an external connectingwiring 1202 provided to fit the element substrate 601, an externalconnecting electrode 1203 formed at the same time as the first electrodelayer 608 serving as the pixel electrode of the display portion 103, aterminal electrode 1204 formed using the same conductive layer as thesource and drain electrode layers of the thin film transistor 604, andan anisotropic conductive film 1205. Note that in FIG. 12B, in additionto the external connecting electrode 1203 and the terminal electrode1204, insulating layers corresponding to a gate insulating film of thethin film transistor 604 and an interlayer insulating layer are stackedon the element substrate 601. The external connecting electrode 1203 iselectrically connected to a terminal of the external connecting wiring1202 through the anisotropic conductive film 1205.

An IC formed using a single crystal semiconductor film or apolycrystalline semiconductor film is mounted on a substrate which isseparately prepared and connected to the external connecting wiring1202. The IC separately formed and the external connecting electrode1203 may be connected to each other through the external connectingwiring 1202 by any method such as COG, wire bonding, or TAB.

In the cross section of the bent portion 1201 obtained by bending thedisplay device illustrated in FIG. 12B, the element substrate 601 andthe external connecting wiring 1202 are provided to fit each other. As aresult, the contact area of the element substrate 601 and the externalconnecting wiring 1202 can be increased, resulting in an increase in theadhesive strength therebetween.

In the display portion 103 in FIG. 12B, as in FIGS. 7A and 7B and FIGS.8A and 8B, an electrophoretic element using a microcapsule, anelectrophoretic element of a powder system, a light-emitting element, ora liquid crystal element can be used as the display element instead ofthe twisting ball.

This embodiment can be implemented in appropriate combination with thestructures shown in the other embodiments.

Embodiment 4

In this embodiment, an example of a transistor included in the displaydevice will be described with reference to FIGS. 13A to 13D. FIGS. 13Ato 13D illustrate examples of the thin film transistor that can be usedas the thin film transistor 604 in Embodiment 3.

In FIGS. 13A to 13D, an insulating film 1301 is formed over the elementsubstrate 601, and the thin film transistor 604 is provided over theinsulating film 1301. An insulating layer 1302 and the insulating layer607 are formed over the thin film transistor 604, and the firstelectrode layer 608 is provided to be electrically connected to the thinfilm transistor 604.

The thin film transistor 604 illustrated in FIG. 13A has a structure inwhich wiring layers 1303 a and 1303 b serving as source and drainelectrode layers are in contact with a semiconductor layer 1304 withoutan n⁺ layer interposed therebetween.

The thin film transistor 604 illustrated in FIG. 13B is a bottom-gatethin film transistor in which a gate electrode layer 1305, a gateinsulating layer 1307, the semiconductor layer 1304, n⁺ layers 1306 aand 1306 b serving as source and drain regions, and the wiring layers1303 a and 1303 b serving as the source and drain electrode layers areprovided over the element substrate 601 having an insulating surface,and over the insulating film 1301. The n⁺ layers 1306 a and 1306 b aresemiconductor layers each having a lower resistance than thesemiconductor layer 1304.

The n⁺ layers 1306 a and 1306 b may be provided between the gateinsulating layer 1307 and the wiring layers 1303 a and 1303 b.Alternatively, the n⁺ layers may be provided both between the gateinsulating layer and the wiring layers and between the wiring layers andthe semiconductor layer.

The thin film transistor 604 illustrated in FIG. 13C is a bottom-gatethin film transistor in which source and drain electrode layers are incontact with a semiconductor layer without an n⁺ layer interposedtherebetween.

The gate insulating layer 1307 exists in the entire region including thethin film transistor 604 illustrated in FIG. 13C, and the gate electrodelayer 1305 is provided between the gate insulating layer 1307 and theelement substrate 601 having an insulating surface. The wiring layers1303 a and 1303 b are provided over the gate insulating layer 1307.Then, the semiconductor layer 1304 is provided over the gate insulatinglayer 1307 and the wiring layers 1303 a and 1303 b. Although notillustrated, a wiring layer is provided over the gate insulating layer1307 in addition to the wiring layers 1303 a and 1303 b, and the wiringlayer extends beyond the perimeter of the semiconductor layer 1304.

The thin film transistor 604 illustrated in FIG. 13D is a top-gate thinfilm transistor. The semiconductor layer 1304 including the n⁺ layers1306 a and 1306 b serving as source and drain regions is formed over theelement substrate 601 having an insulating surface, and over theinsulating film 1301. The gate insulating layer 1307 is formed over thesemiconductor layer 1304, and the gate electrode layer 1305 is formedover the gate insulating layer 1307. In addition, the wiring layers 1303a and 1303 b serving as source and drain electrode layers are formed incontact with the n⁺ layers 1306 a and 1306 b. The n⁺ layers 1306 a and1306 b are semiconductor regions each having a lower resistance than thesemiconductor layer 1304.

Although a single-gate transistor is described in this embodiment, amulti-gate transistor such as a double-gate transistor may also be used.In that case, a gate electrode layer may be provided above and below thesemiconductor layer, or a plurality of gate electrode layers may beprovided only on one side of (above or below) the semiconductor layer.

There is no particular limitation on the semiconductor material used forthe semiconductor layer. Examples of the material used for thesemiconductor layer of the thin film transistor will be described below.

As a material for the semiconductor layer included in the semiconductorelement, it is possible to use an amorphous semiconductor (hereinafter,also referred to as an AS) that is formed by sputtering or vapor-phasegrowth using a semiconductor material gas typified by silane or germane,a polycrystalline semiconductor that is obtained by crystallizing theamorphous semiconductor by utilizing light energy or thermal energy, amicrocrystalline semiconductor (also referred to as a semi-amorphous ormicrocrystal semiconductor, and hereinafter, also referred to as anSAS), or the like. The semiconductor layer can be deposited bysputtering, LPCVD, plasma CVD, or the like.

Considering Gibbs free energy, the microcrystalline semiconductor filmis in a metastable state that is intermediate between an amorphous stateand a single crystal state. That is, the microcrystalline semiconductoris in a third state that is stable in terms of free energy, and hasshort-range order and lattice distortion. Columnar or needle-likecrystals grow in the direction of the normal to the surface of thesubstrate. The Raman spectrum of microcrystalline silicon, which is atypical example of a microcrystalline semiconductor, is shifted to alower wavenumber side than 520 cm⁻¹ that represents single crystalsilicon. In other words, the Raman spectrum of microcrystalline siliconhas a peak between 520 cm⁻¹ that represents single crystal silicon and480 cm⁻¹ that represents amorphous silicon. Furthermore, themicrocrystalline semiconductor film contains 1 atomic % or more ofhydrogen or halogen to terminate dangling bonds. The microcrystallinesemiconductor film may further contain a rare gas element such ashelium, argon, krypton, or neon to further promote lattice distortion,whereby a favorable microcrystalline semiconductor film with improvedstability can be obtained.

This microcrystalline semiconductor film can be formed by ahigh-frequency plasma CVD method with a frequency of several tens ofmegahertz to several hundreds of megahertz, or a microwave plasma CVDapparatus with a frequency of 1 GHz or more. Typically, themicrocrystalline semiconductor film can be formed using silicon hydride,such as SiH₄, Si₂H₆, SiH₂Cl₂, or SiHCl₃, or silicon halide, such asSiCl₄, or SiF₄, which is diluted with hydrogen. Furthermore, themicrocrystalline semiconductor film can be formed with a gas containingsilicon hydride and hydrogen which is diluted by one or more kinds ofrare gas elements selected from helium, argon, krypton, and neon. Insuch a case, the flow rate ratio of hydrogen to silicon hydride is setto 5:1 to 200:1, preferably, 50:1 to 150:1, and more preferably, 100:1.

The amorphous semiconductor is typified by hydrogenated amorphoussilicon, and the crystalline semiconductor is typified by polysilicon orthe like. Polysilicon (polycrystalline silicon) includes so-calledhigh-temperature polysilicon that contains polysilicon formed at aprocess temperature of 800° C. or higher as its main component,so-called low-temperature polysilicon that contains polysilicon formedat a process temperature of 600° C. or lower as its main component, andpolysilicon formed by crystallizing amorphous silicon by using, forexample, an element that promotes crystallization. It is needless to saythat a microcrystalline semiconductor or a semiconductor partiallyincluding a crystalline phase can also be used as described above.

As a semiconductor material, a compound semiconductor such as GaAs, InP,SiC, ZnSe, GaN, or SiGe as well as silicon (Si) or germanium (Ge) alonecan be used.

In the case of using a crystalline semiconductor film for thesemiconductor layer, the crystalline semiconductor film may bemanufactured by various methods (e.g., laser crystallization, thermalcrystallization, or thermal crystallization using an element such asnickel that promotes crystallization). Alternatively, a microcrystallinesemiconductor, which is an SAS, may be crystallized by laser irradiationto increase crystallinity. In the case where an element that promotescrystallization is not introduced, before being irradiated with laserlight, an amorphous silicon film is heated at 500° C. for one hour in anitrogen atmosphere, whereby hydrogen contained in the amorphous siliconfilm is discharged to allow its concentration to be 1×10²⁰ atoms/cm³ orless. This is because, if the amorphous silicon film contains muchhydrogen, the amorphous silicon film is broken by laser irradiation.

There is no particular limitation on a method for introducing the metalelement into an amorphous semiconductor film as long as the metalelement can exist on the surface of or inside the amorphoussemiconductor film. For example, sputtering, CVD, plasma processing(including plasma CVD), an adsorption method, or a method of applying ametal-salt solution can be employed. Among them, the method using asolution is simple and easy, and is useful in terms of easyconcentration adjustment of the metal element. At this time, an oxidefilm is preferably deposited at the surface of the amorphoussemiconductor film by UV light irradiation in an oxygen atmosphere,thermal oxidation, treatment with ozone-containing water or hydrogenperoxide including a hydroxyl radical, or the like in order to improveits wettability and to spread the solution on the entire surface of theamorphous semiconductor film.

In the step of crystallizing an amorphous semiconductor film to form acrystalline semiconductor film, an element that promotes crystallization(also referred to as a catalytic element or a metal element) may beadded to the amorphous semiconductor film and heat treatment (at 550° C.to 750° C. for 3 minutes to 24 hours) may be performed forcrystallization. As the element that accelerates (promotes)crystallization, it is possible to use one or more kinds of elementsselected from iron (Fe), nickel (Ni), cobalt (Co), ruthenium (Ru),rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), platinum (Pt),copper (Cu), and gold (Au).

In order to remove or reduce the element that promotes crystallizationof the crystalline semiconductor film, a semiconductor film containingan impurity element is formed in contact with the crystallinesemiconductor film so as to function as a gettering sink. As theimpurity element, an impurity element imparting n-type conductivity, animpurity element imparting p-type conductivity, a rare gas element, orthe like can be used. For example, it is possible to use one or morekinds of elements selected from phosphorus (P), nitrogen (N), arsenic(As), antimony (Sb), bismuth (Bi), boron (B), helium (He), neon (Ne),argon (Ar), krypton (Kr), and xenon (Xe). A semiconductor filmcontaining a rare gas element is formed in contact with the crystallinesemiconductor film containing the element that promotes crystallization,and then heat treatment is performed (at 550° C. to 750° C. for 3minutes to 24 hours). The element promoting crystallization which iscontained in the crystalline semiconductor film moves into thesemiconductor film containing a rare gas element, and thus the elementpromoting crystallization which is contained in the crystallinesemiconductor film is removed or reduced. After that, the semiconductorfilm containing a rare gas element, which has functioned as a getteringsink, is removed.

The amorphous semiconductor film may be crystallized by a combination ofthermal treatment and laser light irradiation. Alternatively, eitherthermal treatment or laser light irradiation may be performed pluraltimes.

A crystalline semiconductor film can also be formed directly over thesubstrate by a plasma method. Alternatively, a crystalline semiconductorfilm may be selectively formed over the substrate by a plasma method.

It is also possible to use an oxide semiconductor such as zinc oxide(ZnO) or tin oxide (SnO₂) for the semiconductor layer. In the case ofusing ZnO for the semiconductor layer, a gate insulating layer can beformed of Y₂O₃, Al₂O₃, TiO₂, a stack thereof, or the like, and a gateelectrode layer, a source electrode layer, and a drain electrode layercan be formed of ITO, Au, Ti, or the like. In addition, In, Ga, or thelike may be added to ZnO.

As the oxide semiconductor, a thin film represented by InMO₃ (ZnO)_(m)(m>0) can be used. Note that M denotes one or more of metal elementsselected from gallium (Ga), iron (Fe), nickel (Ni), manganese (Mn), andcobalt (Co). For example, M is gallium (Ga) in some cases, and in othercases, M contains other metal elements in addition to Ga, such as Ga andNi or Ga and Fe. Furthermore, the above oxide semiconductor may containFe, Ni, another transition metal, or an oxide of the transition metal asan impurity element in addition to the metal element contained as M. Forexample, an In—Ga—Zn—O-based non-single-crystal film can be used as theoxide semiconductor layer.

An oxide semiconductor layer (InMO₃(ZnO)_(m) film (m>0)) in which M isanother metal element may be used instead of the In—Ga—Zn—O-basednon-single-crystal film. Besides the above, the following oxidesemiconductors can be used for the oxide semiconductor layer: anIn—Sn—Zn—O-based oxide semiconductor; an In—Al—Zn—O-based oxidesemiconductor; a Sn—Ga—Zn—O-based oxide semiconductor; anAl—Ga—Zn—O-based oxide semiconductor; a Sn—Al—Zn—O-based oxidesemiconductor; an In—Zn—O-based oxide semiconductor; a Sn—Zn—O-basedoxide semiconductor; an Al—Zn—O-based oxide semiconductor; an In—O-basedoxide semiconductor; a Sn—O-based oxide semiconductor; a Zn—O-basedoxide semiconductor; and an In—Ga—O-based oxide semiconductor.

This embodiment can be implemented in appropriate combination with thestructures shown in the other embodiments.

Embodiment 5

In this embodiment, specific examples of the application of the displaydevice shown in the above embodiments will be described.

FIG. 14A illustrates a portable information terminal including a mainbody 3001, display portions 3002 and 3003, a storage medium 3004,operation switches 3005, and the like. The display device shown in theabove embodiments can be applied to a display device including thedisplay portion 3003 formed using a flexible substrate. Since the shapeof the display portion can be designed freely in such a manner, aportable information terminal with a desired shape can be manufactured.Furthermore, the display device shown in the above embodiments has adriver circuit or a connecting portion between circuits which isunlikely to be damaged; thus, a robust display device can be provided.

FIG. 14B illustrates an example of an e-book reader provided with thedisplay device shown in the above embodiments. A first housing 3101includes a first display portion 3102 and operation buttons 3103, asecond housing 3104 includes a second display portion 3105, and thefirst housing 3101 and the second housing 3104 can be opened and closedwith a supporting portion 3106. Such a structure allows the e-bookreader to be operated like a paper book. In addition, when the displaydevice shown in the above embodiments is applied to the first displayportion 3102 and the second display portion 3105, a driver circuit or aconnecting portion between circuits is unlikely to be damaged; thus, arobust e-book reader can be provided.

FIG. 15A illustrates a display device 1502 used for an advertisement ina vehicle such as a train 1501. In the case where an advertising mediumis printed paper, the advertisement is replaced by hands; however, byusing a display device performing display with a display element, theadvertising display can be changed in a short time with less manpower.Furthermore, stable images can be obtained without display defects. Inaddition, when the display device shown in the above embodiments isapplied to the display device 1502, a driver circuit or a connectingportion between circuits is unlikely to be damaged; thus, a robustdisplay device for an advertisement can be provided.

FIG. 15B illustrates a display device 1511 used for an outdooradvertisement. The movement of the display device 1511 manufacturedusing a flexible substrate increases an advertisement effect of adisplay portion 1512 as an advertising medium. The advertisement isreplaced by hands; however, by using a display device performing displaywith a display element, the advertising display can be changed in ashort time. Furthermore, stable images can be obtained without displaydefects. In addition, when the display device shown in the aboveembodiments is applied to the display portion 1512, a driver circuit ora connecting portion between circuits is unlikely to be damaged; thus, arobust advertisement medium can be provided.

This embodiment can be implemented in appropriate combination with thestructures shown in the other embodiments.

This application is based on Japanese Patent Application serial no.2009-160382 filed with Japan Patent Office on Jul. 7, 2009, the entirecontents of which are hereby incorporated by reference.

What is claimed is:
 1. A display device comprising: an element substratehaving flexibility, the element substrate including a first portion, asecond portion and a third portion, the third portion being adjacent tothe first portion; a display portion provided over the first portion ofthe element substrate; and an external connecting electrode providedover the second portion of the element substrate, wherein the externalconnecting electrode is in contact with an external connecting wiring,and wherein the element substrate is bent so that the externalconnecting electrode and a part of the external connecting wiring aresandwiched between the second portion of the element substrate and thethird portion of the element substrate.
 2. The display device accordingto claim 1 further comprising: a supporting portion covering the secondportion of the element substrate, wherein the supporting portioncomprises a driver circuit for driving the display portion, and whereinthe driver circuit is electrically connected to the external connectingwiring.
 3. The display device according to claim 1, wherein a displayelement included in the display portion is an electrophoretic element, aliquid crystal element, or a light-emitting element.
 4. A display devicecomprising: an element substrate having flexibility, the elementsubstrate including a first portion and a second portion; a sealingsubstrate having flexibility; a display portion provided over the firstportion of the element substrate; and an external connecting electrodeprovided over the second portion of the element substrate, wherein theelement substrate has a larger area than the sealing substrate; andwherein the external connecting electrode is in contact with an externalconnecting wiring, and wherein the element substrate is bent so that theexternal connecting electrode and a part of the external connectingwiring are sandwiched by the element substrate.
 5. The display deviceaccording to claim 4 further comprising: a supporting portion coveringthe second portion of the element substrate, wherein the supportingportion comprises a driver circuit for driving the display portion, andwherein the driver circuit is electrically connected to the externalconnecting wiring.
 6. The display device according to claim 4, wherein adisplay element included in the display portion is an electrophoreticelement, a liquid crystal element, or a light-emitting element.
 7. Adisplay device comprising: an element substrate having flexibility, theelement substrate including a first portion and a second portion; adisplay portion provided over the first portion of the elementsubstrate; and an external connecting electrode provided over the secondportion of the element substrate, wherein the external connectingelectrode is in contact with an external connecting wiring, and whereinthe element substrate is bent so that the external connecting electrodeand a part of the external connecting wiring are sandwiched by theelement substrate.
 8. The display device according to claim 7 furthercomprising: a supporting portion covering the second portion of theelement substrate, wherein the supporting portion comprises a drivercircuit for driving the display portion, and wherein the driver circuitis electrically connected to the external connecting wiring.
 9. Thedisplay device according to claim 7, wherein a display element includedin the display portion is an electrophoretic element, a liquid crystalelement, or a light-emitting element.